Kyle, there are a few things that strike me. First, it is critical that you are in fact receptive to being fucked. It appears you are. You seem to want to enjoy it. So that is half the battle. If you don't want it. It will never work out.
Second, Alec has provided some very sound advice. Pay attention to it.
Third, you obviously have some trust issues, which isn't surprising since you had a previous boyfriend gangrape you with his friends. I'm willing to bet that right now you are telling yourself, "You don't know what you are talking about. I trust him." Here's my answer. If you truly trusted him you wouldn't have these considerable worries that he's going to cheat on you. Trust is trust, dude. If you don't trust him not to cheat on you, than I'm not sure you truly trust him enough for anal sex, especially with your background. I'm not blaming you!!! It isn't your fault! but it is something you are going to have to work through with him. First off, talk to him and let him know all your feelings in the matter, including your insecurities that he's going to cheat on you. Communication and mutual expression of feeling is how we develop trust. It will take time.
Personally, I don't know how you were raped (and frankly, I don't want to know, but it looks like it was both oral and anal. BTW, from your pics, you look absolutely adorable. Raping you, would be like beating a puppy. Just plain wrong! Not that rape is ever right, mind you, but I think you get the point.). I suggest you start off with oral sex, and make sure you are in control. He shouldn't be putting his hands on your head at all, at first. You said you had a problem with precum. Then focus on the shaft and balls and tentatively move to the head of his penis. You don't have to be an expert at BJ's over night. Take your time. Have him talk to you about how pleasurable it is for him. Hopefully, you will begin to associate the act with him rather than with that previous asshole boy friend. I'm no psychiatrist so I don't know any fancy mental tricks here. But I think that might work.
As for anal sex, I suggest letting him use a dildo, but plug or what ever on you first. Perhaps, you should do it to yourself first even. Start with something small and work your way up over time. When you are comfortable, let him use it on you. That way, you get the feeling of him penetrating you, without actually fucking you. It is penetration without the physical domination. Over time, and with enough lube and fingering, you should desensitize yourself to it, so you don't associate the feeling back to the rape. When you try bottoming again try to make sure that you don't use any of the positions used when you were raped. You on top is good in that allows you control. But make sure you look into his eyes so it becomes about him.
It will all take time. I suggest that you do NOT just let him pound you. You won't enjoy it and you will only make the situation worse in that you will only reinforce the associations of helplessness and pain with bottoming. Yes it will hurt some, no doubt, but it should be managable. Lastly, try to take a bath ahead of time, that can help loosen things up a bit too.